The present invention generally relates to medical retrieval devices for capturing material such as stones within a body and to medical retrieval devices featuring a basket which captures one or more stones located in a body tract and which optionally fragments, crushes, or releases the stones.
Medical retrieval devices for capturing stones in a body tract generally include a basket. Some medical retrieval baskets are also mechanical lithotriptors which optionally crush or fragment stones that are too large to be removed intact from the body tract after the stone has been captured within the basket. One type of known device for crushing or breaking stones in a body tract has a wire basket that is typically introduced into a body tract via a working channel of an endoscope or by means of a guidewire.
Baskets designed for mechanical retrieval are typically constructed from a plurality of wires that are arranged and shaped such that their natural form, when unrestrained, is to expand radially outward. The basket wires are gathered together at their distal ends and at their proximal ends to form a basket. An elongated traction member typically extends from the basket through a sheath to a handle.
A typical retrieval basket is introduced into a body tract via an endoscope or catheter and maneuvered around the stone until the stone enters the basket. If it is necessary to reduce the size of the stone, it is then fragmented typically by applying tension to the basket wires surrounding the stone until sufficient force is applied directly to the stones by the basket wires to cause the stone to break apart.
Mechanical limitations and wide variation in the size, location, shape, and composition of stones in the body present problems in retrieving stones in a body tract. Methods that are used to reduce the size of the stone include lithotripsy such as by acoustic shock waves delivered to the stone from within or outside the body, laser energy applied directly to the stone, or compressive force applied to the stone by means of a mechanical basket. If mechanical basket lithotripsy is attempted on a stone composed of very hard material, the basket wire tension required to fragment the stone may exceed the strength of the basket wires, the various connecting joints of the medical device, the elongated traction member attached to the basket base, or the sheath. If the path of the body tract is very tortuous, the bends in the body tract will cause intimate contact of the traction member with the interior surface of the sheath. The friction generated between the traction member and the sheath will cause the tension applied to the proximal end of the traction member to be greatly reduced when delivered to the basket wires. It is possible for the mechanical strength of the basket wires, the various connecting joints in the device, the traction member, or the sheath to be exceeded even when fragmenting stones of only moderately hard composition.
Failure of the medical retrieval device, including the retrieval basket or any of its components, following capture of a stone may require release of the stone before the basket can be withdrawn from the body tract. Failure of a medical device may occur, for example, near the proximal end of a traction member impairing the ability of the operator to manipulate the basket from the proximal end of the device to remove the basket and captured stone from the body tract. Alternatively, the traction member may fail at the distal end of the device. The broken end of the traction member may traumatize the lining of the body tract if an attempt is made to withdraw the failed device from the body tract. If one or more of the basket wires fail, it may be impossible to remove the basket via the same route by which the basket was introduced into the body tract without traumatizing the lining of the body tract with the fragmented ends of the broken basket wires.
With most known retrieval baskets, it is difficult to disengage the stone from the basket so that the basket can be removed from the body tract. Retrieval baskets typically lack sufficient strength to break the stone. Attempts to perform lithotripsy may result in failure of the device, including failure of the retrievable basket or any of its components. If the stone can not be released from the basket, more invasive surgical approaches are required to disengage the stone from the basket and to remove the basket and stone from the body tract.
It is an object of the invention to provide a medical device useful for retrieval of one or more stones and/or other calculi, objects, or other material from a body tract of a patient, such as biliary and pancreatic ducts, hepatic ducts, cystic duct, common bile duct, ureters, urinary bladder, urethra, and kidney.
Further, it is an object of the invention to provide a medical device capable of fragmenting a stone or other object in a body tract of a patient prior to removal. Finally, it is an object of the invention to provide a medical device capable of safe disengagement from the object being retrieved or fragmented and subsequent safe withdrawal of the device in case of failure of any of the components thereof during the procedure.
Accordingly, a medical device having a multi-wire retrieval basket which is releasable when an amount of force that is less than the amount of force required to cause failure of components of the retrieval device other than the tip joint is applied to the wires of the basket is disclosed herein.
In general, in one aspect, the invention features a medical device comprising a handle, a sheath, and a basket. The sheath, having a lumen formed therein, distally extends from the handle. In one embodiment of the invention, the basket consists of a plurality of wires having a proximal end and a distal end. The proximal ends of the basket wires are joined at a basket base and the distal ends of the basket wires are releasably joined by a tip joint. An elongate traction member may be axially disposed within the lumen of the sheath. In one embodiment, the traction member distally extends from the proximal end of the handle and is connected to the basket base. The traction member may comprise a cable, a coil, a shaft, a guidewire or a mandril wire. In one embodiment, the traction member and the basket wires may be formed from a single piece of material. In another embodiment, the proximal ends of the basket wires are joined at the basket base to the traction member by a proximal connector.
The tip joint is releasable from the distal end of the basket wires when the predetermined force, which is less than the force required to cause the traction member or at least one basket wire to fail, is applied to the tip joint.
Embodiments of this aspect of the invention include the following features. The tip joint may comprise an adhesive joint, a solder joint, a welded joint or an over-molding joint. In one embodiment, the tip joint comprises a tubular tip member. The lumen of the tubular tip member is adapted to receive the distal end of the basket therein. In a particular embodiment, the lumen of the tubular tip member is compressed around the basket wires thereby securing the distal end of the basket therein. At least one wire of the plurality of wires forming the basket is capable of sliding out of the tubular tip member when the predetermined force is applied to the tubular tip member so that the tubular tip member deforms. The predetermined force is less than the force required to cause the traction member or at least one wire of the plurality of wires forming the basket to fail. In one embodiment, the tubular tip member is made of, for example, sterling silver, silver, gold, platinum, stainless steel, or a nickel titanium alloy. In other embodiments, the tubular tip member is made of plastics.
In one embodiment of the invention, the basket is moveable between a withdrawn position in which the basket is collapsed within the lumen of the sheath, and an expanded position in which the basket extends from the distal end of the sheath and is disposed outside of the lumen for capturing the objects in the body. Movement of the basket between the expanded position and the withdrawn position causes the objects in the body captured in the basket to fragment.
In one embodiment of the invention, the handle includes at least one actuating mechanism. In a particular embodiment, the traction member is slideably moveable relative to the sheath when actuated by the actuating mechanism in the handle, which causes the traction member to shift the basket between the withdrawn position and the expanded position.
In another embodiment of the invention, the sheath is slideably moveable relative to the traction member. In this embodiment, the sheath is connected to the actuating mechanism at the handle, which causes the sheath to shift the basket between the withdrawn position and the expanded position.
The handle of the device according to the invention may be detachable. In one embodiment, the sheath is dimensioned to fit within a working channel of an endoscope. In one embodiment, the plurality of wires forming the basket is made of, for example, stainless steel or a nickel titanium alloy.
In general, in another aspect, the invention features a method for removing objects from a body tract, including the steps of providing a medical device as described above, introducing the medical device with the basket in the withdrawn position into the working channel of the endoscope; accessing the target body tract; shifting the basket into the expanded position; manipulating the basket to capture the objects therein; and withdrawing the medical device from the body tract. In a particular embodiment of this aspect of the invention, the method further includes the step of applying traction to the traction member in the proximal direction thereby generating tension within the basket and causing the captured objects to fragment. In another embodiment, the method further includes the step of applying traction to the sheath in the distal direction thereby generating tension within the basket and causing the captured objects to fragment. In some embodiments, the method also includes the step of injecting contrast material for fluoroscopic visualization.